1. Field of the Invention
The present invention relates to a mobile communication technology, and more particularly, to a method for transmitting uplink signals.
2. Discussion of the Related Art
In a mobile communication system, a User Equipment (UE) may receive information from an evolved Node B (eNB) on a downlink and transmit information to the eNB on an uplink. The UE transmits or receives data and various pieces of control information. There are many physical channels depending on the types and usages of the transmitted or received information.
FIG. 1 illustrates physical channels used in a mobile communication system, for example, a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system and a general signal transmission method using the physical channels.
Referring to FIG. 1, upon power-on or when a UE initially enters a cell, the UE performs an initial cell search involving synchronization of its timing to an eNB in step S101. For the initial cell search, the UE may be synchronized to the eNB and acquire information such as a cell Identifier (ID) by receiving a Primary Synchronization CHannel (P-SCH) and a Secondary Synchronization CHannel (S-SCH). Then the UE may receive broadcast information from the cell on a Physical Broadcast CHannel (PBCH). In the mean time, the UE may determine a downlink channel status by receiving a DownLink Reference Signal (DL RS) during the initial cell search.
After the initial cell search, the UE may acquire more specific system information by receiving a Physical Downlink Control CHannel (PDCCH) and receiving a Physical Downlink Shared CHannel (PDSCH) based on information of the PDCCH in step S102.
On the other hand, if the UE has not completed connection to the eNB, it may perform a random access procedure to complete the connection in steps S103 to S106. For the random access, the UE may transmit a predetermined sequence as a preamble to the eNB on a Physical Random Access CHannel (PRACH) in step S103 and receive a response message for the random access on a PDCCH and a PDSCH corresponding to the PDCCH in step S104. In the case of contention-based random access other than handover, the UE may perform a contention resolution procedure by further transmitting the PRACH in step S105 and receiving a PDCCH and its related PDSCH in step S106.
After the foregoing procedure, the UE may receive a PDCCH and a PDSCH in step S107 and transmit a Physical Uplink Shared CHannel (PUSCH) and a Physical Uplink Control CHannel (PUCCH) in step S108, in a general downlink/uplink signal transmission procedure.
FIG. 2 is a block diagram of the UE for processing an uplink signal for transmission.
Referring to FIG. 2, a scrambler 201 of the UE may scramble a transmission signal with a UE-specific scrambling signal in order to transmit the uplink signal. A modulation mapper 202 modulates the scrambled signal to complex symbols in Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), or 16-ary Quadrature Amplitude Modulation (16QAM) according to the type of the transmission signal and/or a channel status. A transform precoder 203 processes the complex symbols and a resource element mapper 204 may map the processed complex symbols to time-frequency resource elements, for actual transmission. The mapped signal may be transmitted to the eNB through an antenna after being processed in a Single Carrier-Frequency Division Multiple Access (SC-FDMA) signal generator 250.
FIG. 3 is a block diagram of the eNB for processing a downlink signal for transmission.
Referring to FIG. 3, in the 3GPP LTE system, the eNB may transmit one or more codewords on the downlink. Therefore, the one or more codewords may be processed to complex symbols through scramblers 301 and modulation mappers 302 in the same manner as for the uplink transmission illustrated in FIG. 2. A layer mapper 303 maps the complex symbols to a plurality of layers. A precoder 304 may multiply the layers by a precoding matrix selected according to a channel status and allocate the multiplied layers to respective antennas. Resource element mappers 305 may map the transmission signals for the respective antennas to time-frequency resource elements. The mapped signals may be transmitted through the respective antennas after being processed in Orthogonal Frequency Division Multiple Access (OFDMA) signal generators 306.
In the mobile communication system, Peak-to-Average Ratio (PAPR) may be more problematic for uplink transmission from the UE than for downlink transmission from the eNB. That's why the uplink signal transmission is carried out in SC-FDMA, while OFDMA is employed for the downlink signal transmission, as described above with reference to FIGS. 2 and 3.
FIG. 4 is a block diagram illustrating SC-FDMA for uplink signal transmission and OFDMA for downlink signal transmission in the mobile communication system.
Referring to FIG. 4, the UE and the eNB commonly have a Serial-to-Parallel Converter (SPC) 401, a subcarrier mapper 403, an M-point Inverse Discrete Fourier Transform (IDFT) processor 404, and a Parallel-to-Serial Converter (PSC) 405, for uplink and downlink signal transmissions, respectively. In addition to these components, the UE further includes an N-point Discrete Fourier Transform (DFT) processor 402 for transmitting a signal in SC-FDMA, such that the transmission signal takes single-carrier characteristics by canceling the effects of the IDFT of the M-point IDFT processor 404 to some degree.
In the above-described mobile communication system, the UE transmits uplink control information in a predetermined frequency band different from that of uplink data. The uplink control information transmission may be implemented in various manners. Some control information may be transmitted periodically at a predetermined interval, whereas other control information may be transmitted non-periodically upon request of the eNB.
If the UE transmits data and control information simultaneously, a certain process is required to maintain the afore-mentioned SC-FDMA characteristics in the mobile communication system.